SpaceX's Polaris Dawn crew returns to Earth victorious, making huge gains in Elon Musk's plans to send humans to Mars

• SpaceX's Polaris Dawn crew has returned to Earth.
• Elon Musk's dreams of building a city on Mars got a major boost from the Polaris Dawn mission.
• They tested spacesuits, radiation exposure, and Starlink space-laser communications for Mars travel.

SpaceX's Polaris Dawn crew successfully returned to Earth on Sunday, bringing Elon Musk one step closer to his dream of settling Mars.

The five-day mission saw the four commercial astronauts complete a list of historic firsts: They traveled further than anyone has gone in more than 50 years, since the last Apollo missions . The two female crew members, in particular, set the record for the farthest any woman has traveled in space.

They donned new SpaceX spacesuits that had never been tested in orbit, opened their ship to the vacuum of space, and conducted the first-ever commercial spacewalk .

On top of that, they exposed themselves to high levels of space radiation, much higher than what astronauts aboard the International Space Station undergo in the same time period. And they endured a fiery plummet back to Earth.

It was all in the name of paving the way to Mars .

If you ask Jared Isaacman , the billionaire who funded and commanded the mission, it was also in the name of raising funds for childhood-cancer research at St. Jude Children's Research Hospital.

As he previously told Business Insider, before his first flight with SpaceX in 2021, he wanted to "take care of some of the problems that we have here on Earth, so we earn the right to go and explore among the stars."

But the technical aspects of the mission — the spacewalk, the spacesuits, the laser Starlink communication, flying through a radiation belt — were critical tests of technologies SpaceX will need in order to fly humans to the red planet .

Isaacman's future plans fit the Mars bill, too. He's planning two more Polaris missions and says the third one will ditch Crew Dragon for Starship . That's the Statue-of-Liberty-sized mega-rocket SpaceX is developing in South Texas for the express purpose of colonizing Mars.

Mars trailblazers return home

As the Crew Dragon hurtled back toward Earth, plowing through the atmosphere, superheated plasma roared at the edges of its protective heat shield.

Isaacman had done this before, but it was the first spaceflight for the three other crew members: a former US Air Force pilot named Scott Poteet and two SpaceX engineers , Anna Menon and Sarah Gillis.

They felt a jerk as the spaceship deployed parachutes to drift down into the Gulf of Mexico near Florida's Dry Tortugas. It bobbed in the waves, looking like a toasted marshmallow, until a ship hauled it on board and SpaceX workers helped the crew off.

Five days after launch, they had officially completed the most daring crewed commercial spaceflight yet .

Spacewalks and spacesuits for Mars

The main event of the mission was its spacewalk.

The crew spent 48 hours slowly depressurizing their spacecraft so that they could open the hatch to the vacuum of space, sending Isaacman and Gillis out to gaze over Earth and conduct a few mobility exercises.

They were testing SpaceX's new extravehicular spacesuits , designed for the purpose of leaving a spacecraft to conduct maintenance or repairs — an ability that future Mars-bound people will need, since the journey takes months.

"It might be 10 iterations from now and a bunch of evolutions of the suit," but someday someone may even wear a version of these spacesuits " walking on Mars ," Isaacman said in a prelaunch briefing in August.

"There's going to be an armada of Starships arriving on Mars at some point in the future," he added. "Those people are going to have to be able to get out of it and walk around and do important things."

Radiation on the way to Mars

Polaris Dawn also tackled another big challenge for crewed Mars missions: extreme radiation exposure. People traveling to Mars would be exposed to immense amounts of space radiation for months.

So the Crew Dragon spacecraft flew through two donuts of intense radiation surrounding Earth, called the Van Allen belts. The crew conducted tests and measurements to see how it affected their bodies.

"If we get to Mars someday, we'd love to be able to come back and be healthy enough to tell people about it," Isaacman said in August.

Other medical experiments on the mission checked their eyes, veins, and airways, to help SpaceX better understand the impacts of long-distance spaceflight.

Communications for Mars

Polaris Dawn also tested laser-based communications using Starlink, the network of internet satellites that SpaceX has built throughout Earth's orbit.

The commercial astronauts posted on X mid-mission, saying they'd uploaded their photos there using Starlink internet.

Those space lasers lay the groundwork for future communications with deep-space missions — that is, as the Polaris website says, "for missions to the moon, Mars and beyond."

Isaacman seems to be vested in making that happen.

"I'd certainly like my kids to see humans walking on the moon and Mars and venturing out and exploring our solar system," he said ahead of the launch.